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Apparatus and method for measuring spacing

Apparatus and method for measuring spacing description/claims

1. Field of the Invention

The present invention relates to an apparatus and a method for measuring a spacing between an object to be measured and a transparent object. More particularly, the present invention relates to an apparatus and a method for measuring a minute spacing between, for example, a magnetic head and a magnetic recording medium.

2. Description of the Related Art

In recent years, a spacing between a magnetic recording medium (e.g., a hard disk, a magnetic tape, etc.) and a head has been decreased with an increase in the recording density of the magnetic recording medium. Recently, in some case, the spacing is as minute as 5 to 10 nm.

Magnetic tapes have various applications, such as audio tapes, video tapes, computer tapes, and the like. Particularly, in the field of data backup tapes, as the capacity of a hard disk to be backed up is increased, tapes having a storage capacity of several hundreds of gigabytes per roll have been on the market. In the future, the capacity of the backup tape will be unavoidably increased so as to support the increasing capacity of hard disks.

Also, it is essentially required to increase a relative speed of a magnetic tape and a head so as to increase an access speed and a transfer rate.

Also, in order to increase the recording density of a magnetic tape, a system employing, as a signal reproduction head, an MB (magnetoresistance effect) head which causes a current to flow through a magnetoresistance effect film and detects a change in the resistance as a voltage, is used instead of a system employing a conventional electromagnetic induction type (inductive) magnetic head. The output of the MR head can be increased by designing a film having a large change in resistance of the element, a current density, and a head structure.

In the system employing the MR head, since an electromagnetic induction type head is generally employed for recording, an inductive/MR compound head in which a recording head and a reproduction head are integrated together is employed.

In order to increase the storage capacity per roll and support the high relative speed of a magnetic tape and a head as described above, there are two types of magnetic tapes: one in which the recording density is increased (the recording wavelength, and the track width are reduced) by modifying a magnetic layer by improving the magnetic characteristics and dispersibility of ferromagnetic powder; and the other in which the recording capacity is increased by increasing the tape length per roil by reducing the total thickness of the tape. In addition to these, it has been required to improve contact between a magnetic tape and a head by optimizing the mechanical characteristics of a non-magnetic support, an undercoat layer, and a magnetic layer.

In such a background, spacing measuring apparatuses have been proposed which measure a spacing between a magnetic tape and a head. The spacing measuring apparatus is generally based on white-light interferometry, in which a transparent object (simulated head) formed of a light transmitting material is disposed, facing a magnetic tape, and the intensity of interference light at the facing portion is measured.

FIG. 7 is a diagram showing an exemplary configuration of a conventional spacing measuring apparatus. Light emitted from a light source 100 is passed through an optical lens 101a and is then beat by 90 degrees by a half mirror 102. The bent light is passed through an optical lens 101b and is then brought through a simulated head 103 onto a magnetic tape T.

Interference light between reflected light from a surface facing the magnetic tape T of the simulated head 103 and reflected light from the magnetic tape T is transferred through the optical lens 101b, the half mirror 102, and an optical lens 101c to a CCD camera 104 (sensor). The interference light, which has reached the CCD camera 104, is converted into an electrical signal, which is input to an operation apparatus 105. In the operation apparatus 105, based on a relational expression between interference light intensities and spacings, a spacing h corresponding to a interference light intensity which is based on an input electrical signal is calculated.

By using the apparatus employing this method, a spacing of as small as about 150 nm can be relatively correctly measured. However, it is difficult to measure a spacing smaller than that level. Therefore, a further improved measurement apparatus which can measure a still smaller spacing has been proposed (e.g., JP H8-507384A and JP H10-267623A).

In recent high recording density media, the surface of the magnetic layer is finished considerably smooth so as to improve short-wavelength recording characteristics, and a spacing between a magnetic tape and a head has become considerably small. Therefore, it has become necessary to measure a spacing of several tens of nanometers to 10 nm or less.

However, regarding interference light measurement, the technique proposed in JP H8-507384A for calibrating the intensity and determining the order of interference fringes, can measure a spacing of about no less than several tens of nanometers and has difficulty in measuring a spacing smaller than that level.

In the case of the technique proposed in JP H10-267623A for analyzing a change in light intensity in consideration of the spectral intensity distribution of illumination light when a minute distance is measured using the interference light as a reference, it is also difficult to measure a spacing of 100 nm or less.

Therefore, in these techniques, it is difficult to measure a spacing with respect to recent high density recording media which require measurement of a spacing of, for example, 10 nm or less.

The present invention is provided so as to solve the conventional problems as described above. An object of the present invention is to provide an apparatus and a method for measuring a minute spacing of, for example, 10 nm or less.

In order to achieve the object, the present invention provides an apparatus for measuring a spacing between an object to be measured and a transparent object, in which the transparent object is disposed, fading a surface of the object to be measured, light is emitted to impinge through the transparent object onto the object to be measured, and the spacing is calculated based on an intensity of interference light occurring in a facing portion between the surface of the object to be measured and the transparent object. The apparatus comprises a light source for emitting light, a modulator for modulating an intensity of the emitted light with modulation waves having a predetermined frequency, a sensor for converting the light intensity of the interference light into an electrical signal, and a synchronous demodulator for subjecting the electrical signal to synchronous demodulation using the modulation waves as reference waves.

The present invention also provides a method for measuring a spacing between an object to be measured and a transparent object, in which the transparent object is disposed, facing a surface of the object to be measured, light is emitted to impinge through the transparent object onto the object to be measured, and the spacing is calculated based on an intensity of interference light occurring in a facing portion between the surface of the object to be measured and the transparent object. The method comprises modulating an intensity of the emitted light with modulation waves having a predetermined frequency, converting the light intensity of the interference light into an electrical signal, and subjecting the electrical signal to synchronous demodulation using the modulation waves as reference waves.

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